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NiV stress control utilizing PVD with an Ar / N2 gas mixture

Keywords: NiV, stress, PVD

Physical Vapor Deposition (PVD) is a commonly used technique for back side metallization (BSM). The BSM stacks are used in various semiconductor devices, including standard bipolar and high performance power and discrete devices. Cutting edge BSM stacks require good silicon adhesion, low contact resistance and low intrinsic stress. Nickel Vanadium (NiV) is commonly used as a barrier layer in these BSM stacks. As a non-magnetic material, NiV is more suitable for magnetron sputtering than pure Ni, which is magnetic. NiV also tends to be sputtered in a high stress state and high stress in thin films has often degraded adhesion, resulted in long term reliability problems, and bowed thinned wafers.

NiV films deposited by PVD using argon (Ar) process gas are usually under tensile stress. In these cases, film stress can be controlled by various means during the PVD process: deposition temperature, deposition pressure, and RF bias applied to the wafers during deposition. This paper explores how changing the process gas from pure Ar to a mixture of argon and nitrogen gasses can control film stress. Stress neutral NiV(N) films were achieved by adding up to 40% of nitrogen to Ar/N2 mixture. Stress, deposition rate, and sheet resistance were studied as a function of nitrogen percentage in the process gas mixture. Electrical and barrier properties of the resulting NiV(N) films were found to be comparable or better than NiV films deposited with a pure Ar process.